The need has been recognized in the past to furnish ink to a printing plate at a rate which varies along the axis of the printing cylinder, from one column position to the next, in accordance with the ink demand in the respective column positions.
Column-to-column variation in ink feed has been accomplished most commonly by providing a series of adjusting keys spaced along the length of the blade in the ink fountain, thereby producing longitudinal variation in the ink which is picked up from the fountain roller and which flows as merged ribbons of controlled thickness to the point where the ink is transferred from the form roller to the plate. Alternatively, in pressurized ink feed systems, ink is fed at different rates to wide nozzles arranged end-to-end in the longitudinal dimension.
However printing presses, both lithographic and of the letter press type, even of modern design, do not include means for varying the feeding of ink in accordance with need about the periphery, as contrasted with longitudinal dimension, of the plate cylinder. By way of an extreme example, there may be need to print a sheet, of which the top half has a high printing density, requiring heavy inking, while the bottom half contains no printing at all. Yet in a conventional printing press the feed rate in the inking system would be the same for all peripheral portions of the sheet, requiring the press operator to compromise between starvation of ink in the top half of the sheet and a flooding condition in the lower.
I have discovered that it is possible to vary the amount of ink fed at successive peripheral portions of a printing plate by varying the instantaneous velocity of a vibrated roller in the ink feed path, preferably a vibrated roller which is in ink-feeding relation to the form roller. More specifically I have found that the amount of ink transmitted by a vibrated roller tends to be inversely related to the instantaneous velocity of the vibrated roller. Thus, taking the example given immediately above of a sheet having a high printed density in the top half but not printed at all in the lower, the vibrated roller is caused to move with a relatively low axial velocity in creating the ink film which is utilized for printing of the top half of the sheet and moved at a relatively high axial velocity during times phased with passage of the lower portion of the sheet, thereby preventing buildup of non-utilized ink and creation of an incipient flooding condition.
In the past it has been common practice to maintain the form roller axially stationary and to utilize one or more vibrated rollers in the series of rollers which furnishes the ink film to the form roller for smooth merging of adjacent ribbons of ink having different thickness. However I have found that the present invention, namely, variation in ink flow inversely with instantaneous variation in axial velocity, may be achieved by vibration of the form roller itself, in a press of the lithographic type, without causing objectionable smearing of the ink between the printing and non-printing areas.
Not only does a conventional inking system fail to provide variation in ink flow in accordance with peripheral need, but conventional vibrating means, including cranks, swash plates or pneumatic drives, generally have a variation in velocity, for example, sinusoidal in the case of a crank or swash plate drive, such that the instantaneous velocity bears no relation to the peripheral variation in ink requirement and, indeed, in many cases the velocity variation may be directly contrary to the requirement of ink at localized areas.
To summarize, it is an object of the present invention to provide means for varying the flow of ink to a plate mounted on a printing cylinder so that the ink deposited in successive peripheral portions of the plate is in a thickness tailored to the need in each such portion.
It is a related object of the invention to provide means for varying the amount of ink supplied to a printing cylinder which is both simple and economical and which does not require any increase in the number of rollers in the ink feed path.
It is a further object of the present invention to provide means for controlling the instantaneous velocity of a vibrated roller in an ink feed path in accordance with peripheral variations in printing density of the particular plate being used. In this connection it is an object to provide a control board for establishing a succession of sources of control signal corresponding to printing density in which individual control elements are provided settable in vertial columns so that the setting thereof at levels tailored to variations in printing density provides a visual profile corresponding to the ink needs of the plate from the leading edge to the trailing edge.